Soil organic carbon(SOC)and total nitrogen(N)concentrations from bulk soils and soil particle size fractions in the different extent of desertified farmlands(potential, light, medium, severe, and most severe desertified farmlands)were examined to quantitatively elucidate losses of carbon and nitrogen and its mechanisms in the desertification process. Particle size fractions(2 -0.1 mm, 0.1 - 0.05 mm, <0.05 mm)were obtained by granulometric wet sieving from 30 sandy soils(0 - 15cm depth)of different desertified extent. It was shown that soil physical stability index(St)in most severe desertified farmlands was 5 -7% and St in other farmlands was less than 5 %, which contributed to very low soil organic matter content. This was the intrinsic cause that sandy farmlands in Horqin sandy land was subject to risk of desertification. Desertification resulted in considerable losses of SOC and N. Regression analysis indicated that SOC and N content reduced 0.169 g kg-1 and 0.0215 g kg-1 respectively with one percen Soil organic carbon (SOC) and total nitrogen (N) concentrations from bulk soils and soil particle size fractions in the different extent of desertified farmlands (potential, light, medium, severe and most severe desertified farmlands) were examined to quantitatively elucidate losses of Particle size fractions (2 -0.1 mm, 0.1-0.05 mm, <0.05 mm) were obtained by granulometric wet sieving from 30 sandy soils (0-15 cm depth) of different desertified extent. It was shown that soil physical stability index (St) in most severe desertified farmlands was 5 -7% and St in other farmlands was less than 5%, which contributed to very low soil organic matter content. This was the intrinsic cause that sandy farmlands in Horqin sandy land was subject to risk of desertification. Desertification resulted in considerable losses of SOC and N. Regression analysis indicated that SOC and N content reduced 0.169 g kg-1 and 0.0215 g kg- ly with one percen